Specialty pigments have been developed for use in security applications, such as anti-counterfeiting devices printed on banknotes, packaging of high-value items, seals for containers, and even for direct application to commercial items. For example, the U.S. twenty-dollar Federal Reserve Note currently uses optically variable ink. The number “20” printed in the lower-right corner of the face of the note changes color as the viewing angle changes. This is an overt anti-counterfeiting device. The color-shifting effect is not reproducible by ordinary color photocopiers, and someone receiving a note can observe whether it has the color-shifting security feature to determine the note's authenticity.
Other high-value documents and objects use similar measures. For example, iridescent pigments or diffractive pigments are used in paints and inks that are applied directly to an article, such as a stock certificate, passport, original product packaging, or to seals that are applied to an article. Security features that are more difficult to counterfeit are desirable as counterfeiters continue to become more sophisticated.
One anti-counterfeiting approach uses microscopic symbols on multi-layer color-shifting pigment flakes. The symbols are formed on at least one of the layers of the multi-layer color-shifting pigment flakes by a local change of an optical property(s), such as reflectivity. The multi-layer color-shifting pigment flakes generally include a Fabry Perot-type structure having an absorbing layer separated from a reflective layer by a spacer layer. The reflective layer is typically a layer of metal, which renders the pigment flake essentially opaque. If a large portion of these types of pigment flakes are mixed with other pigment, the resultant color might be significantly different from the pigment, and if too few of these flakes are mixed with other pigment, they might be difficult to find.
Another technique uses epoxy-encapsulated shaped flakes of polyethylene terephthalate (“PET”). A reflective layer is deposited on a roll of PET, and then the PET is cut into pieces. The flakes are coated or encapsulated with epoxy to improve the durability of the reflective layer. These flakes are available in a variety of shapes, such as square, rectangle, hexagon, and “apostrophe,” and a selection of reflective metallic tints, such as silver, pewter, gold, and copper. However, the epoxy layer and the relatively thick PET substrate (which typically has a minimum thickness of about 13 microns (0.5 mils) for use in vacuum deposition processes) result in a relatively thick flake, typically greater than 14 microns. Unfortunately, such a thick flake is not desirable for use in covert applications where the thickness is substantially greater than the base pigment. Similarly, such thick flakes do not flow well in inks, and create lumps in paint. When paint includes a thick flake that creates a rough surface, a relatively thick clear topcoat is typically applied over the rough surface.
It is desirable to mark objects with covert anti-counterfeiting devices that overcome the limitations of the techniques discussed above.
This invention relates to providing flakes which have taggents or covert symbols stamped or embossed or etched therein by mechanical means or formed by laser means, wherein the covert symbols can be seen with a microscope. In order to preserve the integrity of the symbols, a frame is provided around all of or part of covert symbols so that when the individual flakes are removed from the support structure they are deposited on, the majority of flakes break along the frame lines provided instead of breaking in a less controlled unpredictable manner wherein break lines would otherwise occur with greater frequency through and about the symbols. To further attempt to ensure that breakage occurs along frame lines or grooves, the frames grooves may have a different profile than the grooves defining the covert symbols, wherein the frame grooves are designed to break or crack more readily than the covert symbol grooves. In some instances parallel frame lines may be provided so that the flakes break into a ribbon; in a preferred embodiment of this invention, flakes and more particularly one or more symbols within a flake will have a framed grooved border on more than four or fewer sides about the one or more symbols, so that the flakes break in uniform squares or rectangles along the frame lines. Of course triangular or hexagonal flakes may be provided as well in this manner, by pre-framing symbols on three sides, prior to removing the flakes from their backing. A conventional release layer is provided so that the flakes can easily be removed from their backing or support layer and so that upon removal, the flakes break up along the framing lines. Frames can be made in a similar manner in which the symbols are made; using a laser, etching or stamping of the film that is upon the substrate; in a preferred embodiment, the frames are provided in the same process along with the formation of the symbols.
The term “embossed flakes” used hereafter describes flakes which are embossed by application of pressure to a flake with an embossing tool, or to flakes which are formed on an embossed substrate by being coated upon the embossed substrate, taking the form of the substrate.
It is therefore an object of this invention, to provide flakes having symbols thereon, and wherein the symbols have or had, frames or borders embossed, etched or lasered into the flake or the flake molded from an embossed temporary support, for protecting the symbols during the process of separating flakes from their temporary support backing and wherein the frame grooves are deeper and/or more fracturable than the grooves defining indicia or symbols within a frame.
It is an object of this invention to provide frame grooves that have a different cross sectional profile than the indicia grooves and wherein the frame grooves are designed to break or crack more readily than the indicia grooves.
In another aspect of the invention, the substrate is pre-metalized before adding a release layer to it. After flakes are separated from the release layer the embossed substrate can be cut up into reflective flakes rather than being reused to provide another batch of coated flakes. The pre-metalized substrate can be severed into lengthwise strips to make a new security device (i.e a thread) that contains the same matching design as the flakes produced with the substrate.
In another aspect of the invention, the “sized” flakes after removal from the substrate and properly post process to produce the shaped/symboled flakes are encapsulated to improve the durability of the flakes against breakage during printing or painting applications.